1. Field of the Invention
The present invention relates to a water-cooling system for a water-cooled horizontal cylinder engine which is installed with the axes of a crank shaft and a cylinder thereof disposed to be horizontal, in the transverse direction for the former and in the forward and backward direction for the latter.
2. Background of the Prior Art
A conventional water-cooled horizontal cylinder engine, as depicted in FIG. 5, such as the one shown in Japanese Patent Publication No. 35408, 1982, has a radiator 103 and a fuel tank mounted over the foreside and the backside of a cylinder block 100 laid sideways in a water-cooled horizontal cylinder engine E. A radiator fan 104 is mounted at, for example the left side of the radiator 103 located at the front upper side of the cylinder block 100 and a cooling air passage is provided so as to run through the radiator fan 104 in the left and right direction over the cylinder block 100.
However, in the above-mentioned prior art, since the horizontal cylinder engine E has a radiator 103 mounted thereon, the total height of the engine E becomes large corresponding to that of the radiator 103.
Further, since a cylinder head 105 of the horizontal cylinder engine E is disposed at the front lower section of the engine E, it takes position remote from and downward with respect to the radiator fan 104 which is located at the upper and fore section of the engine E. Hence the cylinder head 105 is not cooled well directly by the cooling air flow delivered by the radiator fan 104, and much heat generated from the cylinder head 105 is not radiated effectively around the engine E but tends to be confined close thereto.
On the other hand, in an engine of the type shown in FIG. 6 and in a water-cooled vertical cylinder engine as shown in U.S. Pat. No. 4,122,353, since a radiator 103a is arranged at the foreside of the engine E instead of the upper side thereof the problem of the total height of the engine of the type having a radiator mounted thereon becomes serious as mentioned above.
However, since such a water-cooled vertical cylinder engine has a cylinder head 105a secured on the upper side of the cylinder block, it is relatively high originally and, further, the height of the radiator 103a is limited correspondingly by that of the cylinder head 105a because upper and lower tanks 113a, 113b of the radiator 103a are connected to a water jacket of the engine E through a hot water pipe 116 and a cold water pipe 117. The overall height of this engine cannot be reduced remarkably in comparison with that of the horizontal cylinder engine.
It is desirable that the overall height of the engine be reduced by shifting the radiator 103a downward, so that the upper tank 113a of the radiator 103a is located below the cylinder head 105a. However, since the upper tank 113a of the radiator 103a is located below the cylinder jacket, it becomes necessary to force downward by means of a water pump opposite to the natural convection, the hot water which tends to ascend due to its decreased density after its completion of heat exchange. As a result, the cooling water is hindered from circulating smoothly and the cooling performance is degraded.